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Caddisflies Laying Eggs

9-3 caddisfly eggs & larvae 402Most caddisflies lay their eggs in or near ponds or streams. A very few species (in the family of northern case makers, Limnephilidae) deposit their eggs above the water on aquatic vegetation in a one- to-two-inch-long mass of jelly (some species’ eggs lack the jelly). Up to 800 eggs (the tan spots within the jelly in yesterday’s post) are laid at one time in one mass. Depending on the species, the eggs take from several weeks up to ten months to hatch. These masses are usually situated so that once the eggs hatch, the larvae will drop down into the water, where they will spend their larval and pupal stages.

Caddisflies are closely related to butterflies and moths, and one of the features they have in common is that the larvae have silk glands in their lower lip. Thanks to the ability to spin silk, the caddisfly larvae build portable cases or attached retreats out of natural material that is available. Some species build elongate tubes out of pieces of plants, sand, sticks or pebbles and reside in them while they drag them along with them wherever they go. Other species attach their cases with silk to crevices in or the bottom of stones in streams. Each species of caddisfly larva always constructs the same type of case, so that you can often tell the genus or even species of caddisfly by the appearance of its case.

The larval stage of a caddisfly can last two to three months or up to two years, depending on the species. Most species spend the winter as active larvae. When it is ready to pupate, the larva attaches its case with silk to something immoveable, such as a large rock. Inside its case, the larva spins a cocoon and eventually pupates inside of it. In two to three weeks the sharp-jawed pupa cuts its way out of its cocoon and floats up to the surface of the water where it emerges as a winged adult, often using its pupal skin as a raft for support during this process. Adult caddisflies live for about 30 days, during which time the males form mating swarms to attract females. After mating takes place, the egg-laying begins.

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6 responses

  1. judilindsey

    Totally cool! Thanks, Judi

    September 3, 2015 at 7:31 am

  2. Ellen Blanchard

    Hi Mary,
    Do you know the name of the water plant species that the Caddis fly eggs are attached
    to in your picture?

    September 3, 2015 at 9:31 am

    • Hi Ellen,
      I want to say Canada goldenrod. I also found some on boneset that was growing near the edge of the pond, but I think these were on goldenrod.

      September 3, 2015 at 1:11 pm

  3. Thanks so much for this one, Mary! I’d taken photos of this kind of blob on a leaf, possibly Alder, at a swampy spot in rural eastern Prince Edward Island. I was completely stumped as to what it might be and didn’t know where to start looking, so was pretty excited to see this mystery photo. Re the plant, not sure if it matters what it is, so long as it’s over water. Thanks again, Barry

    September 3, 2015 at 3:10 pm

  4. The first time I observed a caddisfly larva in our pond, I thought I was watching some sort of an alien/monster – all these little shreds of grasses and what-not moving up and down an underwater stem. When I looked them up, I was amazed at this adaptation. Since then, I have enjoyed finding and watching similar ones in ponds, and the pebbly ones in streams. BUT it seems that I’ve been seeing fewer of them stuck to the bottoms of rocks in streams over recent years – is this something anyone else has noticed?

    September 3, 2015 at 6:21 pm

  5. I think caddisflies are supposed to be pretty good indicators of water quality, but I’m not sure what exactly in the water it is that they are sensitive to.

    September 18, 2015 at 3:24 pm

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